Electrical water purification systems, such as those employed in recreational environments including swimming pools, spas, hot tubs, etc., typically employ a pair of spaced apart electrodes to which a controlled voltage is applied for causing an introduction of metallic ions into the water which kills organic impurities in the water. The subsequent charge potential of the organic impurities causes the dead impurities to be attracted to one another for form large particles that are removed by filtration. With the passage of time the ionization process results in the formation of deposits on the anode which must be removed. For this purpose the polarity of the ionization potentials applied to the electrodes is reversed for a prescribed period of time to cause the deposits to be driven off. In such systems the degree or extent of purification is normally controlled by adjusting the magnitude of the ionization voltage applied to the electrodes; typically the adjustment mechanism involves the controlled insertion of voltage dropping resistors between a large DC power supply and the electrolysis electrodes. Such an adjustment mechanism has a number of drawbacks, not the least of which is the waste of energy.
More particularly, while the adjustment mechanism is a necessary expedient, allowing the quantity of injected ions (and consequently degree of water purification) to be varied in accordance with application and water conditions, the use of a bank of fixed resistors to set the potential level at the ionizing electrodes means that adjustability can be varied only in coarse increments, and the generation of lower valued potentials requires a substantial (heat producing and wasted) IR drop in the voltage dropping circuit. This effectively continuous heating of the dropping resistors eventually causes both circuit and hardware fatigue.